I'm not sure about all the answers to this, but the myelin sheath can get destroyed and plaques can form in the brain that they call MS or ALS. The body has to be cleaned out by colon cleansing and Liver Flushing that will allow the whole body to clean itself out. Wheat germ oil is good for rebuilding the myelin sheaths.
parasites poison the body with their waste products and can cause alteration in ability to absorb nutrition and probably use it to advantage. Fungus can alter brain function and is responsible for panic attacks. From what I've read it eats holes in the blood brain barrier and the brain gets the acetaldehyde from the metabolism of yeast fungi. Been there and done it.